The prior art during the assembly process for a power supply assembly is shown as FIG. 1 and FIG. 2, a plastic insulation pad 11, a semiconductor switch 12, a thermal conduction insulation sheet 13 and a heat sink 14 are secured together by using a screw 10. In the prior art, the insulation of a single semiconductor switch is realized mainly by using a single plastic insulation pad in order to prevent the short circuit caused by the conducting between the semiconductor switch and the heat sink.
The disadvantage of this is that the function, that the dust, metal wire and metal powder, and the like, are prevented from existing outside the metal portion of the semiconductor switch, can not be realized. If the metal wire and metal powder are attached on the metal portion of the semiconductor switch, a short circuit will be produced between the semiconductor switch and the heat sink or between the semiconductor switch and the semiconductor switch.